安装Scion浏览器时出错

问题描述

尝试按如下方式安装scion-browser软件包时出现以下错误：

I get the following error when trying to install the scion-browser package as follows:

% cabal install scion-browser-0.2.9
<snipped>
[23 of 23] Compiling Main             ( src/Main.hs, dist/build/scion-browser/scion-browser-tmp/Main.o )

src/Main.hs:31:24:
    No instance for (MonadException BrowserM)
      arising from a use of `getInputLine'
    Possible fix:
      add an instance declaration for (MonadException BrowserM)
    In a stmt of a 'do' block: maybeLine <- getInputLine ""
    In the expression:
      do { maybeLine <- getInputLine "";
           case maybeLine of {
             Nothing -> return ()
             Just line -> do { ... } } }
    In an equation for `loop':
        loop
          = do { maybeLine <- getInputLine "";
                 case maybeLine of {
                   Nothing -> return ()
                   Just line -> ... } }
cabal: Error: some packages failed to install:
scion-browser-0.2.9 failed during the building phase. The exception was:
ExitFailure 1

有什么办法解决此问题吗？

Any idea how to fix this?

谢谢。

推荐答案

问题是更改了使用的 StateT 类型。在 haskeline< 0.7 ，它使用了Control.Monad.State 模块 rel = nofollow> mtl ，在版本0.7.0.0中， haskeline 删除了对 mtl ，并使用直接打包。但这本身就不是问题，因为 mtl 现在只是变形金刚的包装。但是， haskeline 使用的模块是 Control.Monad.Trans.State.Strict ，而 mtl 中的> Control.Monad.State 包裹 Control.Monad.Trans.State.Lazy 。因此，

The problem is that haskeline-0.7.0.0 changed the used StateT type. In haskeline < 0.7, it used the Control.Monad.State module from mtl, in version 0.7.0.0, haskeline dropped the dependency on mtl and uses the StateT monad transformer of the transformers package directly. That would in itself not be a problem, since mtl now is just a wrapper around transformers. However, the module used by haskeline is Control.Monad.Trans.State.Strict, while Control.Monad.State from mtl wraps Control.Monad.Trans.State.Lazy. Thus the

instance MonadException m => MonadException (StateT s m) where
    controlIO f = StateT $ \s -> controlIO $ \(RunIO run) -> let
                    run' = RunIO (fmap (StateT . const) . run . flip runStateT s)
                    in fmap (flip runStateT s) $ f run'

来自 System.Console.Haskeline.MonadException 不再用于 StateT 由使用。

简单的解决方法是将 haskeline 限制为早期版本，

The easy fix is to constrain haskeline to an earlier version,

cabal install --constraint="haskeline < 0.7" scion-browser

另一个解决方法是将 scion-browser 源中的导入更改为 Control.Monad.State.Strict 使其使用 haskeline-0.7.0.0 进行构建。

The other fix would be changing the imports in the scion-browser source to Control.Monad.State.Strict to make it build with haskeline-0.7.0.0.

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